MK3 quick screw-on reverse bowden + connectors

A compact, fully 3d-printed reverse bowden setup compatible with the MK3 or the MK3 Bondtech extruder upgrade.

I designed this after trying out PC4-M6/10 connectors, which I didn't like for the following reasons:

• Straight PC4 connectors cannot be really used without a tube inserted, since the internal blades will oppose the filament moves during retraction. These are fine if you plan to use the reverse bowden all the time, but I wanted something optional without having to swap the PTFE tube with a short section all the time.

• PC4-M6/10 connectors fitted to a screw-on design become unnecessarily tall.

• Twisting the screw with a PC4 connector while holding the tube stationary eats the PTFE tube at the blades. I had a PC4 connector fail due to this.

In this design the bowden attachment is fully optional and can be quickly screwed-on only when required. Fits regular 4mm bowden tubing. Includes a female-female bowden connector for further splicing.

The cover is actually smaller than the original MK3 sensor cover, and requires shortening the internal PTFE tube to a length of 12mm. Internal 45 degree chamfers in all PTFE sections are highly recommended!

The screw and connector require a tight fit on the bowden tube in order to work correctly. The screw includes internal notches to hold onto the tube which require a decent amount of force to overcome. Once fitted though the screw can be rotated while holding the tube stationary as it's held firmly by those.

Due to the bowden tolerances, and to get the right fit, the assembly comes in three variants: tight, medium and large. To find the right tolerance print the connector piece: the bowden tube should require some light pressure to insert and remove. The connector shouldn't disconnect by itself or by simple shaking. To insert the bowden into the screw section push firmly while twisting! The tube should be pushed until it's flush to the internal cavity. Let the tube+screw sit for about an hour after insertion, so that the PTFE tube naturally regains it's original diameter.

STEP files included if further adjustment is required!

Printing

• Sensor cover can be printed with either 0.15 or 0.2mm layer height, 0.4 nozzle.
• Screw and connectors require 0.15mm layer height, 0.4 nozzle.

Using other settings might compromise the tightness of the screw and fit of the bowden tube.